Candy Cladistics
Introduction:
Cladistics groups organisms together by the features, or characteristics, that they
share. Organisms that evolved from the same ancestors have the same shared characteristics,
the same way that you and your siblings probably share the same hair and eye color because
you are descended from the same parents. The relationships of organisms are shown in a
branching diagram called a cladogram.
Assumptions made by cladistics:
 Organisms of a clade are related by descent from a common ancestor.
 Change in characteristics occurs in lineages over time.
The simple cladogram below is an example of how things are grouped together using
cladistics.
tall spiral
spiral shell
shell with one opening
shared characteristics
In a cladogram, the places where the branches meet are called nodes (circles have
been drawn at the nodes in the cladogram above). Every organism at the end of a branch that
comes from the same node is part of the same group, called a clade. The shared
characteristics written next to a node defines the clade that comes off of that node. The same
cladogram is shown below and the clades that come off of each node have been circled. The
name written next to each node is the name of the clade branching from that node.
Moon snail
Marine Gastropods
Conchifers
Gastropods
Clades are usually given names so that they’re easier to refer to. In the snail cladogram,
it’s much easier to name the “Gastropods” than to keep calling it “the clade with the animals that
have spiral shells.” When you define a clade using shared characteristics, you also give it a
name, so that the next time you use the name “Gastropods,” other people know that you’re
talking about “the animals that have spiral shells.” Lots of the groups that you’re familiar with
are probably clades, and you can probably easily think of the shared characteristics that define
these clades.
Notice that the clades that branch from nodes higher up in the tree stack inside the ones
that branch from nodes further down in the tree. Like a set of measuring cups, the smaller
clades (the ones with fewer organisms inside them) fit inside the bigger clades (the ones with
more organisms inside them). The smaller clades are also part of the bigger clades. Think of
the way you are part of this biology class, which is part of this school, which is part of the
Guilford County School system. You belong to all of these groups, which fit one inside the
other.
So an organism that is higher up in the tree belongs to its clade AND to every clade that
comes from a node below it in the cladogram. For example, in our cladogram, the moon snail
belongs to the Gastropod clade AND to the Conchifer clade.
Answer the following on your RIGHT Side in COMPLETE SENTENCES
1. How does cladistics group organisms?
2. What are the assumptions of cladistics?
3. What is a node?
4. What are 3 shared characteristics of mammals?
5. What are 3 shared characteristics of birds?
6. What is the relationship of the organisms higher up on the cladogram?
7. Copy the data table below on your RIGHT side:
Name
plain M&Ms
(M&M
choclatus)
crunchy M&Ms
(M&M crunchius)
Peanut butter
M&Ms (M&M
pbutterus)
Skittles
(Stamped
fruitius)
Dots
(Domehead
fruitius)
Reese’s
(Crunchy
pbutterus)
Hard candy
(Discus
hardius)
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Today we will be figuring out the relationships of a very interesting group of organisms,
the Candylites, and putting them into a cladogram. The 7 species of Candylite we are studying
today:
Materials:
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plain M&Ms (M&M choclatus)
crunch M&Ms (M&M crunchius)
peanut butter M&Ms (M&M pbutterus)
Skittles (Stamped fruitius)
Dots (Domehead fruitius)
Reese’s (Crunchy pbutterus)
Hard candy (Discus hardius)
Procedure:
1. Take the Candylites out of their nest (cup).Study the Candylites carefully and think of a
characteristic that all of them share. Write that characteristics down in Column #1 in your
data table.
2. Now think of a characteristic that 6 of the Candylites share, but that one of them doesn’t
have. Write this characteristic in Column #2
3. In Columns #3-#7 think of other characteristics that they share. The idea being that you
want to sort by deductive reasoning, and make sure that each subsequent column has
characteristics that the others don’t.
4. Put an X in the data table next to each characteristic that is shared.
5. Construct a cladogram (on your LEFT) following the rules:
 All taxa go on the endpoints of the cladogram.
 All cladogram nodes must have one or more derived characteristics that are present in
all taxa above the node.
 All derived characteristicsistics appear on the cladogram only once (unless the
characteristics state originated more than once by convergent evolution).
6. Now the cladogram is finished! The best part of being a systematist (definition: a scientist
that classifies organisms) is naming new groups of organisms! The organisms that share
the same characteristics are part of the same groups, or clades. So for each characteristics
that you’ve come up with, you’ve also come up with a new definition for a new clade. Name
your new clades, preferably choosing names that fit the characteristics you’ve chosen.
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Questions:Answer on your LEFT
1. Based on the classification of Candylites that you performed today, describe the method of
cladistics in your own words.
2. The simplest organism is often at the base of the cladogram. Why do you think this is?
Why do you think that the organism at the base of the cladogram is often called the root?
3. How would you group a pencil, pen, and marker into a cladogram? Put them into the
cladogram below and write down their shared characteristicss next to the nodes.
4. Candylitologists don’t all draw the same cladogram for the Candylites. What is your
hypothesis for why they disagree with one another?
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